太阳能电池冷却用微通道散热器内纳米流体换热特性

该文基于螺旋式微通道散热器,采用Mixture模型对菲涅尔高倍聚光下纳米流体冷却工质的换热特性进行了研究,并引入强化传热因子η来判定冷却工质的换热能效,结果表明:雷诺数相同时,与蒸馏水相比,Al_2O_3-H_2O和Si O2-H_2O纳米流体具有更高的对流换热系数,并且Al_2O_3-H_2O的传热特性要优于SiO_2-H_2O;纳米流体的强化传热因子随着入口流速的增大呈先升高后降低的趋势,当入口流速为0.82 m/s时,强化传热因子达到最大值,但质量分数为5%的Al_2O_3-H_2O纳米流体的强化换热因子与流体的入口速度成正比,且当流体速度小于0.68 m/s时,其强化传热因子高于其他3种纳米流体;Al_2O_3-H_2O纳米流体的换热特性随着纳米粒子粒径的增加而降低,随着质量分数的增加呈先增后降的二次曲线趋势,当质量分数为5.5%时换热特性最强,该研究为纳米流体在高倍聚光砷化镓太阳能电池冷却方面提供理论参考。

Heat transfer characteristics of nanofluid in microchannel applied on solar cell cooling

Nanofluid is an innovative heat transfer fluid with superior potential for enhancing the heat transfer performance of fluids.Recent developments in nanotechnology indicate that the nanofluid is an efficient working fluid and coolant in the solar thermal application.In this paper, heat transfer characteristics of several kinds of the nanofluids as the cooling medium were studied via Mixture multiphase models in Fresnel high concentration system based on the helix microchannel cooling structure, which was used to simulate the reduction of the temperature of GaAs cell with the nanofluid as cooling medium.And the enhancement heat transfer factor was introduced to determine the heat transfer efficiency of the cooling medium.The experimental results showed that the temperature of the microchannel inlet crosssection with the nanofluid as the cooling medium was lower than the distilled water as the cooling medium.Meanwhile, other various factors also affected the microchannel heat transfer characteristics including the mass fraction, particle size and the particle type of the nanofluid.The results displayed that the heat transfer characteristics of Al2O3-H2O nanofluid increased with the increase of the mass fraction.When the mass fraction was 5.5%, Nusselt number of the nanofluid reached the maximum value.But when the mass fraction was more than 5.5%, the Nusselt number decreased and tended to remain in a stable value around 3.23.Nusselt number of the Al2O3-H2O nanofluid decreased with the particle size increasing with the same mass fraction.The heat transfer capability of the nanofluid decreased when the mass fraction of Al2O3-H2O nanofluid was larger than 5.5%, which was mainly attributed to the resistance effect of the viscosity over the high heat conducting ability of the nanofluid.Nusselt number of all the fluids which were the distilled water, the different mass fractions of Al2O3-H2O nanofluid and SiO₂-H2O nanofluid increased with the increases of their Reynolds number, and Nusselt number of the nanofluid was greater than the distilled water''s.Nusselt number of nanofluid increased along with the increases of the mass fraction with the same Reynolds number, and the Nusselt number of Al2O3-H2O was greater than of SiO₂-H2O, which meant that the heat transfer characteristics of the Al2O3-H2O nanofluid was better than that of SiO₂-H2O nanofluid.The enhancement heat transfer factor of the nanofluids increased with the growing of the inlet velocity.When the inlet velocity was 0.82 m/s, the enhancement heat transfer factor of Al2O3-H2O (1%) nanofluid and SiO₂-H2O nanofluid both reached the maximum.But the enhancement heat transfer factor of Al2O3-H2O nanofluid with the mass fraction was 5% which was proportional to the inlet velocity, and the optimum enhancement heat transfer factor of Al2O3-H2O(5%) nanofluid was obtained compared with all kinds of the nanofluids when the velocity of nanofluid was lower than 0.68 m/s.Furthermore, the enhancement heat transfer factor of the same kind of nanofluid increased with the mass fraction increasing as the same inlet velocity, and the enhancement heat transfer factor of Al2O3-H2O nanofluid was higher than that of SiO₂-H2O nanofluid.The heat transfer characteristic of Al2O3-H2O nanofluid decreased with the particle size growing.This work provided a theoretical reference for the nanofluids applied in the GaAs solar cell cooling under high concentration.